In a solid-oxide fuel cell assembly, a sealing gasket is disposed between spaced, parallel components and includes a gas-filled pillow structure formed in the general shape of the manifold opening to be sealed. The gasket acts as a passive gas spring that responds with increased seating force to increased temperature. The gasket comprises first and second elements formed from sheet or foil metal stock having mating concavities and joined along their mutual surfaces to form the gas-filled pillow structure in the shape of each opening to be sealed. The first and second elements are respectively formed of the same material as the components and diffusion bonded on their outer surfaces to their respective component surfaces.